Is this your first pair of headphones? I really only have one (the KRK KNS 8400), and they are mine too. I was actually just about to post a review on them. Not sure if it will be of any use to you or not, but it's another beginner's experience if you want to read one.

Now, I'm not really asking for opinions on the headphones, per-se (but you can leave yours).

It's come to these choices.

Audio Technica ATH-M50 ~ $110

KRK KNS-8400 ~ $100

Sony MDR-V6 ~ $60

Sennheiser HD 280 ~ $70

These are all big names, with, as far as I can tell, a rather close following of each.

What I'm wondering is:

Since I don't have a quality A/V store nearby to test these cans myself, I was thinking of buying ALL of them, testing them on my own time, and then reselling the ones I don't want.

Purchases are probably going to be made on eBay, since I have the highest chance of getting a good deal, as well as being able to resell them for (maybe) a profit.

SO....Is this a really GOOD idea? Or a really TERRIBLE idea, which will result in my sadness and death?

And of course, If I do this, there will be a comparison review as well as a log of the experience.

It is a decent idea: you can resell the KNS 8400 for 80-90, M50 for 110 in a few months, and the other two, you may eat a little bit when reselling. Speaking strictly for myself, headphones that sell for less than $75 are those that I would rather buy new, since the price difference between used and new isn't that significant. Of course, there will be people who will want to buy those off of you for a decent discount.

It really is up to you: how much are you willing to lose in this investment/experiment? If I may also ask, what made you narrow down to those four specific headphones?

Heh, I only own 3 pairs of good headphones right now and they're all on your list (I don't have V6's).

The 280s were my first pair, and I picked up the m50s and 8400s more recently. Out of the three, I'd probably go with either the m50 or 8400 myself, depending on whether you wanted a more neutral sound with better clarity (8400) or a stronger bass impact (m50). They're both comfortable to my ears, I'd give a slight edge to the 8400 in terms of comfort but give the nod to the m50 in terms of build quality (it feels very solid/durable to the touch).

One other thought OP. There are TONS of people who have the M50. You would be better off posting in the recommendations thread to people who have heard the headphones you have questions on. It is likely you will get lots of M50 fans saying M50 who have never even heard the other phones. I have heard them and I recommend the KRK over the M50 (which I used to own) in every aspect including bass.

On the same token, I've owned the 7506, HD448, KNS8400, M50, M-Audio Q40, Ultrasone PRO900, AKG K550, Shure SRH840, SHR940, Beyerdynamic DT250-250, Beyerdynamic DT770 and have finally settled on the Sennheiser Amperior. I was searching for a headphone for mixing and video editing and have also auditioned the HD280, HD380, AKG K240 and AKG K271. Of all of these, obviously the K550 and Amperior are in another league, but below this, the M50 is the clear winner, along with the DT250. Unfortunately the DT250 is known for its poor quality control and for this reason, I would not recommend them. The M50 is receiving a lot of 'anti-hype' at head-fi these days since the forum has been oversaturated with newbies who praise them without having heard any other headphone but don't let this fool you. The M50 is awesome and despite its age still the clear king of the sub 150$ range.

The Sennheiser HD 280 is a decent sounding headphone, but it is very fragile. The Audio Technica ATH-M50 is much more durable and sounds better.

The KNS 8400 is a bass thumper so if you want extra bass it would be a decent option, but for me the bass is just too much.

If you listen to more rock and roll then something like the AKG K 240 / K271 MKII would be great. If you listen to more techno then the ATH-M50 will deliver more bass, but still keep the midrange and treble in check.